US 2005/0049761 (JP 2004168148A) discloses a vehicle control system that is capable of suppressing the vibrations of a vehicle body. The vehicle control system corrects an input instruction so as to suppress the vibrations of the vehicle by a motion model. The motion model is formed by a dynamic model of the vibrations of tires of the vehicle, the vehicle body unsprung vibrations in suspensions, and the vehicle body sprung vibration which are received by the vehicle body per se, which occurs according to an input instruction corresponding to at least one of accelerator operation, steering operation, and brake operation which are conducted by an occupant.
The above vehicle control system uses vehicle vibration models including a vehicle body sprung vibration model, a suspension vibration model and a tire vibration model. The vehicle vibration model is separated and hierarchized into the vehicle body sprung vibration model, the suspension vibration model, and the tire vibration model, thereby making it possible to express the respective vibration models as lower-order linear models. Here, hierarchization means formation of hierarchical structure in up-down or front-rear transfer of vibration caused by a tire. For this reason, the capacity of storing the vehicle vibration model can be reduced, and the calculation load can be reduced in execution of the estimated calculation of the vibrations that are generated in the respective portions of the vehicle using the vehicle vibration model.
However, when the suspension vibration model and the tire vibration model are separated from each other, the vibration state in the longitudinal (front-back) direction of the tire cannot be estimated with a high precision. This phenomenon will be described below.
When a driving wheel receives a drive torque to rotate, a force (translational force) that propagates in the longitudinal direction of the vehicle occurs in a driving wheel rotating shaft. In fact, the translational forces of the driving wheels are internally propagated to a driven wheel (rolling wheel) side through a chassis to generate the translational force at the driven wheel rotating shaft. In this way, the translational force that is exerted on the driving wheel rotating shaft from the driving wheel affects the motion state of the driven wheels. However, when the tire vibration model and the suspension vibration model (chassis vibration model) are separated from each other, it is impossible to deal with the force that is internally propagated to the driven wheel side from the driving wheel side.